Wireless communications systems are susceptible to errors introduced in the communications link between the transmitter and receiver. Various error mitigation schemes including, for example, error detection, error correction, interleaving, etc. may be applied to control the error rate in the communications link. Error detection techniques employ parity bits to detect errors at the receiver. If an error is detected, then typically the transmitter is notified to resend the bits that were received in error. In contrast, error correction techniques employ redundant bits to both detect and correct bits that were received in error.
The total number of transmitted bits in a codeword is equal to the sum of information bits and redundant bits. The code rate of an error correction code is defined as the ratio of information bits to the total number of transmitted bits. Error correction codes include block codes, convolutional codes, turbo codes, low density parity check (LDPC) codes, and combinations thereof. Turbo codes are popular error correction codes in modern wireless communications systems.
Turbo codes were first introduced in 1993 by Berrou, Glavieux, and Thitimajshima and have been extensively developed since then. Turbo codes provide near-Shannon limit decoding by employing a combination of simpler encoders and an iterative decoding structure which exchanges soft decision information among a plurality of decoders.
Many wireless system are being introduced today such as Long Term Evolution (LTE) as part of the evolution of third generation partnership project (3GPP) systems, Worldwide Interoperability Microwave Access (WiMAX), wideband code division multiple access (WCDMA), evolution-data optimized (EVDO)/cdma2000, etc. These newer wireless systems utilize various forms of turbo encoding and decoding.
Conventional turbo decoding introduces overhead which reduces throughput. Improvements are desired which minimize turbo decoding overhead to allow enhancement of decoder throughput. In addition, a unified turbo decoder architecture which can be employed across a variety of wireless systems such as LTE, WiMAX, WCDMA, EVDO, etc. is desirable.